Commercial or office chairs, and specifically those commonly referred to as secretarial chairs, are generally provided with an adjustment structure for permitting the vertical position of the back to be adjusted to accommodate the user. In the past, many chairs employed a threaded handle arrangement mounted on the chair back and creating a frictional engagement with an upright for vertically adjusting but fixedly securing the chair back. These threaded handle arrangements have been extensively utilized, but have been recognized as being not only unreliable, but more importantly extremely unsightly in view of their protrusion from the rear of the chair back.
Accordingly, in recent years manufacturers have attempted to provide height adjusting mechanisms which are more effectively hidden within the interior of the chair back. Most of these mechanisms, however, have been bulky and/or structurally and mechanically complex. More importantly, most of these mechanisms have been unable to provide secure latching of the chair back to the upright, particularly when the chair back is subjected to an external vertical load, and hence have permitted the chair back to be released permitting undesired vertical displacement of the chair back either upwardly or downwardly. For example, a person standing adjacent a chair may lean against the chair back and hence impose a rather substantial downward force thereon, which force often causes release of the adjusting mechanism, whereupon the chair back moves suddenly downwardly, and hence creates a situation which can cause possible harm to the person or at the least annoyance and inconvenience. Similarly, it has also been discovered that many of the adjusting mechanisms permit the chair back to be released when the chair is lifted upwardly by the back, and again this causes annoyance and inconvenience, and also creates a situation where possible injury can occur.
In recognition of the above problem, and specifically the safety hazard created when the chair back releases upon application of a downwardly-directed external force, the association representing manufacturers of office furniture have required that all chairs employing a vertically adjustable back must be capable of withstanding a downward external load on the back of at least 300 pounds without permitting release of the back. Many known adjusting mechanisms are unable to withstand such load, and while others are capable of withstanding this load, nevertheless even these others are generally of substantial complexity and/or require excessive spring forces which make manual release of the mechanisms extremely difficult. Thus, these known mechanisms are still considered deficient in many respects.
One attempt to provide an improved height-adjusting mechanism is illustrated by U.S. Pat. No. 4,012,158 issued to Harper. The adjusting mechanism disclosed in this patent employs a latching lever pivotally mounted on a support secured to the chair back, which latching lever is spring-urged so that a small tooth thereon is selectively engageable with one of a plurality of notches formed along the outer edge of the upright. These notches slope downwardly as they project toward the outer edge of the upright, and are provided with straight sidewalls. While this known mechanism is desirable in view of its compact and simple structure, nevertheless it has been observed that forming the mechanism with straight-sided notches employing a lever and notch arrangement having the positional arrangement disclosed in this patent is unsatisfactory, since this type mechanism is believed to permit the latching lever to automatically disengage from the notch when an external downward force of substantial magnitude is imposed on the chair back. In addition, the latching finger associated with the lever is extremely small and undersized relative to the notches, so that substantial vertical looseness exists between the latching finger and the notches. This is also undesirable when an upward external force is imposed on the chair back, such as the chair being lifted by the back, since this results in at least a small upward movement of the back so that the finger impacts against the upper sidewall of the notch, and this can cause accidental release of the latching finger and hence release of the chair back.
Accordingly, this invention relates to an improved height-adjusting mechanism for a chair back, which mechanism overcomes the aforementioned disadvantages.
More specifically, the improved height-adjusting mechanism of this invention is desirably simple and compact, and can be effectively hidden within the interior of the chair back so as to not detract from the appearance thereof. At the same time, this improved mechanism permits the chair back to be securely latched or locked in any one of a selected number of discrete vertical positions, with the mechanism maintaining the chair back securely locked even when a substantial upward or downward external load (such as at least 300 pounds) is imposed on the chair back.
The adjusting mechanism of this invention coacts with, and in fact includes part of, the upright which projects upwardly from the chair seat. The upright has an elongated slot extending vertically thereof, and a slide member mounted on the chair back is slidably accommodated within the slot. One of the inner edges of the slot has a series of vertically spaced notches formed therein, which notches open into the slot. An adjustment lever is pivotally mounted on the slide for swinging movement about a substantially horizontal axis, and is spring-urged toward a position of engagement with one of the notches. The latching lever has, at its upper end, a sidewardly-projecting finger for engagement within one of the notches. This latching finger, and each of the notches, is defined by opposed upper and lower edges which are generated on radii which are centered on the pivot axis of the lever, and the finger is sized to snugly fit within and substantially totally fill the notch, whereby imposition of upward or downward external forces on the chair back causes these forces to be resisted over a substantial peripheral area between the latching finger and the notch, which resisting forces are directed radially relative to the pivot axis. This enables the latching lever to be securely maintained in its latched position, even when upward or downward external forces of substantial magnitude are imposed on the chair back.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this type upon reading the following specification and inspecting the accompanying drawings.